1. Field of the Invention
The invention relates to a self-propelled construction machine, in particular a road miller, stabiliser, recycler or surface miner, comprising a machine frame and an operating drum, the operating drum being arranged in a drum housing which is open downwards and is closed on both sides by an edge protector which is adjustable in height. Furthermore, the invention relates to a method for operating such a construction machine.
2. Description of the Prior Art
The above-mentioned construction machines have a rotating operating drum for processing ground material, which can be a milling or cutting drum. By means of the operating drum, for example, damaged road layers can be removed, existing road surfaces can be reprocessed, the land can be prepared for road construction, or mineral resources can be mined.
The operating drum of the known self-propelled construction machines is arranged in a drum housing which is open downwards and is closed by a hold-down device positioned in front of the operating drum in the working direction, and a stripper positioned behind the drum in the working direction. Shields extending in the working direction, which are referred to as edge protectors, close the drum housing at the sides.
The edge protector of the known self-propelled construction machines is adjustable in height relative to the machine frame. For this purpose, a lifting device is provided for raising and/or lowering the edge protector and provides a floating position for the edge protector in which the edge protector can follow height adjustments of the machine frame relative to the ground, for example when changing the milling depth of a road milling machine, or unevennesses in the terrain. In the floating position, the height of the edge protector can be adjusted by the lifting device such that the edge protector automatically lowers onto the surface of the ground from a raised position under its own weight, and after coming into contact with the ground surface, rests on the ground surface with a specified contact force. When the construction machine moves forward, the edge protector is then pulled over the ground. In this case, the edge protector may additionally be loaded with or relieved of a specified force by the lifting device.
The lifting device for raising and/or lowering the edge protector can be operated by the driver of the machine in order to make the operating drum accessible. During operation of the construction machine, however, the edge protector should always be lowered so that the drum housing is closed at the sides. Therefore, self-propelled construction machines have a circuit which does not permit the edge protector to be fixed in the raised position during operation of the machine.
In practice, in particular when driving over loose ground, there is the problem of the edge protector, which rests on the ground with the specified contact force, digging into the ground as the construction machine moves forward. This may lead not only to increased driving resistance and therefore increased fuel consumption, but also to increased wear or deformation of the edge protector. If the edge protector digs deeply into the ground, this may even cause the construction machine to come to a complete standstill.
A self-propelled construction machine which has a lifting device for raising and/or lowering the edge protector, which device provides floating mounting of the edge protector, is known from DE 10 2012 015 346 A1 (U.S. Pat. No. 9,016,798). The lifting device is actuated by a control unit which is configured such that when a specified value for the minimum distance between a reference point on the edge protector and the ground surface is not reached, the lifting device is shifted out of the floating position and the edge protector is raised. As a result, the edge protector is effectively prevented from being able to dig into loose ground. The edge protector comprises a resilient scanning element for scanning the ground surface, which is fastened to the edge protector such that when a specified value for the minimum distance between the reference point and the ground surface is not reached, the scanning element is deflected. The known construction machine works in practice; however, it is disadvantageous that an additional distance sensor is required on the edge protector, the resilient scanning element of which sensor is subjected to mechanical stresses.